Alpha-fetoprotein (AFP)-derived peptides as epitopes for hepatoma immunotherapy: a commentary

Alpha-fetoprotein accelerates the progression of hepatocellular carcinoma by promoting Bcl-2 gene expression through an RA-RAR signalling pathway

Previous studies have found that alpha-fetoprotein (AFP) can promote the proliferation of hepatoma cells and accelerate the progression of hepatocellular carcinoma (HCC). However, the exact mechanism of action remains unclear. Recent bioinformatics studies have predicted the possible interaction between AFP and retinoic acid receptors (RARs). Thus, the purpose of this study was to investigate the molecular mechanism through which AFP promotes tumour cell proliferation by interfering with the RA-RAR signal pathway. Our data indicated that AFP could significantly promote the proliferation and weaken ATRA-induced apoptosis of hepatoma cells. Besides, cytoplasmic AFP interacts with RAR, disrupting its entrance into the nucleus, which in turn affects the expression of the Bcl-2 gene. In addition, knockdown of AFP in HepG2 cells was synchronously associated with an incremental increase of RAR binding to DNA, as well as down-regulation of Bcl-2; the opposite effect was observed in AFP gene-transfected HLE cells. Moreover, a similar effect of AFP was detected in tumour tissues with high serum AFP, but not in adjacent non-cancerous liver tissues, or HCC tissues with low serum AFP levels. These results indicate that AFP acts as signalling molecule and prevents RAR from entering into the nucleus by interacting with RAR, thereby promoting the expression of Bcl-2. Our data reveal a novel mechanism through which AFP regulates Bcl-2 expression and further suggest that AFP may be used as a novel target for treating HCC.

Hepatitis B virus X protein upregulates alpha-fetoprotein to promote hepatocellular carcinoma by targeting miR-1236 and miR-329

Hepatitis B virus (HBV) infection is the most common cause of hepatocellular carcinoma (HCC) worldwide, wherein the expression of alpha-fetoprotein (AFP) is reactivated to promote tumorgenesis. Hepatitis B virus X protein (HBx) protein encoded by the HBV virus X gene has been considered to be oncogenic and implicated in hepatocarcinogenesis. However, the relationship between HBx and abnormal AFP expression in HCC is yet to be fully understood. To explore the potential regulation of HBx on AFP re-expression in HCC, 97 HCC samples of different etiologies were analyzed, and extremely higher serum AFP levels were found in patients with HBsAg⁺ . Analyses of HBV-related HCC specimens showed that the expression of AFP was negatively correlated with the levels of miR-1236 and miR-329. Further analyses indicated that HBx promotes the expression of AFP by orchestrating the levels of miR-1236 and miR-329 both in vitro and in vivo. Specifically, miR-1236 and miR-329 bind to the potential target sequences in AFP mRNA 3'-untranslated region to suppress its expression. HBx transfection resulted in the significant decrement of these microRNAs and increment of AFP expression. Moreover, AFP promotes the proliferation of hepatoma cells and attenuates the proapoptotic effect of chemotherapy agents. These findings revealed a novel regulatory mechanism of HBx on the abnormal AFP expression in HCC, which may provide a therapeutic approach for combating HBV-related HCC by targeting the regulation of AFP expression.

-Catenin peptide vaccines repress hepatocellular carcinoma growth via CD8+ T cell activation

As classical therapy method of advanced hepatocellular carcinoma (HCC) is not effective enough, HCC immunotherapy is a hot spot for research in recent years. Although in recent years, immune checkpoint inhibitors are focused in cancer therapy, vaccines and adoptive cell therapy (ACT), as traditional immunotherapy methods for HCC are still promising. We found that δ-Catenin might be a new tumor-associated antigen for HCC, for it could be upregulated as a stress associated protein under hypoxia and irradiation treatment. δ-Catenin peptide vaccines could inhibit the growth of subcutaneous hepatocellular tumors in vivo. According to our work, δ-Catenin peptide vaccines could stimulate the activation of cytotoxic T lymphocytes (CTLs) and enhance the infiltration of CD8+ T cells into tumors. Moreover, δ-Catenin peptide vaccines could enhance the secretion of IFN-γ and the killing of tumor cells by T cells. Mechanistically, δ-Catenin peptide vaccines, presented by antigen-presenting cells to T cells, could enhance the activation of T cells via MAPK/ERK signaling and the transcriptional factors Eomes and T-bet. Our research results indicate new potential peptide vaccines, which can be applied in clinical HCC therapy.

Icaritin inhibits the expression of alpha-fetoprotein in hepatitis B virus-infected hepatoma cell lines through post-transcriptional regulation

Although it has showed that icaritin can apparently suppress growth of HCC by reducing the level of AFP, the intrinsic mechanism remains unclear. In this study, we explored the possible mechanism of miRNAs on post-transcriptional regulation of AFP gene, as well as the effects of HBV infection and icaritin in hepatoma cells. The results showed that miR-620, miR-1236 and miR-1270 could bind target sites in the range of 9–18 nt and 131–151 nt downstream of the stop codon in the AFP mRNA 3′-UTR to suppress the expression of AFP. Mutation of these target sites could reverse the effects of these miRNAs. Icaritin (10 μM) might reduce the stability and translational activity of AFP mRNA by increasing the expression levels of these mentioned miRNAs. HBV infection resulted in apparent decreases of these miRNAs and, consequently, increased AFP expression. The results indicated that miR-620, miR-1236 and miR-1270 are critical factors in the post-transcriptional regulation of AFP. Icaritin can counteract the effect of HBV. These findings will contribute to full understanding of the regulatory mechanism of AFP expression in hepatoma cells. And also it revealed a synergistic mechanism of HBV infection and elevation of AFP in the pathogenesis of HCC, as well as the potential clinical significance of icaritin on the therapy of HCC induced by HBV.

Cancer vaccines and immunotherapeutic approaches in hepatobiliary and pancreatic cancers

Hepatobiliary and pancreatic cancers along with other gastrointestinal malignancies remain the leading cause of cancer-related deaths worldwide. Strategies developed in the recent years on immunotherapy and cancer vaccines in the setting of primary liver cancer as well as in pancreatic cancer are the scope of this review. Significance of orthotopic and autochthonous animal models which mimic and/or closely reflect human malignancies allowing for a prompt and trustworthy analysis of new therapeutics is underlined. Combinational approaches that on one hand, specifically target a defined cancer-driving pathway, and on the other hand, restore the functions of immune cells, which effector functions are often suppressed by a tumor milieu, are shown to have the strongest perspectives and future directions. Among combinational immunotherapeutic approaches a personalized- and individual cancer case-based therapy is of special importance.

Alpha-fetoprotein and Fanconi Anemia: Relevance to DNA Repair and Breast Cancer Susceptibility

Elevations of serum alpha-fetoprotein (sAFP) have been reported in fetal and infant states of anemia. Fanconi anemia (FA) belongs to a family of genetic instability disorders which lack the capability to repair DNA breaks. The lesion occurs at a checkpoint regulatory step of the G2 to mitotic transition, allowing FA cells to override cell-cycle arrest. FA DNA repair pathways contain complementation groups known as FANC proteins. FANC proteins form multi-protein complexes with BRCA proteins and are involved in homologous DNA repair. An impaired cascade in these events imparts an increased breast cancer susceptibility to female FA patients. Elevations of sAFP have availed this fetal protein to serve as a biomarker for FA disease. However, the origin of the synthesis of sAFA has not been determined in FA patients. We hypothesize that hematopoietic multipotent progenitor stem cells in the bone marrow are the source of sAFP production in FA patients.

A combination hepatoma-targeted therapy based on nanotechnology: pHRE-Egr1-HSV-TK/(131)I-antiAFPMcAb-GCV/MFH

Combination targeted therapy is a promising cancer therapeutic strategy. Here, using PEI-Mn0.5Zn0.5Fe2O4 nanoparticles (PEI-MZF-NPs) as magnetic media for MFH (magnetic fluid hyperthermia) and gene transfer vector for gene-therapy, a combined therapy, pHRE-Egr1-HSV-TK/(131)I-antiAFPMcAb-GCV/MFH, for hepatoma is developed. AntiAFPMcAb (Monoclonal antibody AFP) is exploited for targeting. The plasmids pHRE-Egr1-HSV-TK are achieved by incorporation of pEgr1-HSV-TK and pHRE-Egr1-EGFP. Restriction enzyme digestion and PCR confirm the recombinant plasmids pHRE-Egr1-HSV-TK are successfully constructed. After exposure to the magnetic field, PEI-MZF-NPs/pHRE-Egr1-EGFP fluid is warmed rapidly and then the temperature is maintained at 43 °C or so, which is quite appropriate for cancer treatment. The gene expression reaches the peak when treated with 200 μCi (131)I for 24 hours, indicating that the dose of 200 μCi might be the optimal dose for irradiation and 24 h irradiation later is the best time to initiate MFH. The in vitro and in vivo experiments demonstrate that pHRE-Egr1-HSV-TK/(131)I-antiAFPMcAb-GCV/MFH can greatly suppress hepatic tumor cell proliferation and induce cell apoptosis and necrosis and effectively inhibit the tumor growth, much better than any monotherapy does alone. Furthermore, the combination therapy has few or no adverse effects. It might be applicable as a strategy to treat hepatic cancer.

Hepatoma-Targeted Radionuclide Immune Albumin Nanospheres: (131)I-antiAFPMcAb-GCV-BSA-NPs

An effective strategy has been developed for synthesis of radionuclide immune albumin nanospheres (¹³¹I-antiAFPMcAb-GCV-BSA-NPs). In vitro as well as in vivo targeting of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs to AFP-positive hepatoma was examined. In cultured HepG2 cells, the uptake and retention rates of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs were remarkably higher than those of ¹³¹I alone. As well, the uptake rate and retention ratios of ¹³¹I-antiAFPMcAb-GCV-BSA-NPs in AFP-positive HepG2 cells were also significantly higher than those in AFP-negative HEK293 cells. Compared to ¹³¹I alone, ¹³¹I-antiAFPMcAb-GCV-BSA-NPs were much more easily taken in and retained by hepatoma tissue, with a much higher T/NT. Due to good drug-loading, high encapsulation ratio, and highly selective affinity for AFP-positive tumors, the ¹³¹I-antiAFPMcAb-GCV-BSA-NPs are promising for further effective radiation-gene therapy of hepatoma.

Glycosylation-Based Serum Biomarkers for Cancer Diagnostics and Prognostics

Cancer is the second most common cause of death in developed countries with approximately 14 million newly diagnosed individuals and over 6 million cancer-related deaths in 2012. Many cancers are discovered at a more advanced stage but better survival rates are correlated with earlier detection. Current clinically approved cancer biomarkers are most effective when applied to patients with widespread cancer. Single biomarkers with satisfactory sensitivity and specificity have not been identified for the most common cancers and some biomarkers are ineffective for the detection of early stage cancers. Thus, novel biomarkers with better diagnostic and prognostic performance are required. Aberrant protein glycosylation is well known hallmark of cancer and represents a promising source of potential biomarkers. Glycoproteins enter circulation from tissues or blood cells through active secretion or leakage and patient serum is an attractive option as a source for biomarkers from a clinical and diagnostic perspective. A plethora of technical approaches have been developed to address the challenges of glycosylation structure detection and determination. This review summarises currently utilised glycoprotein biomarkers and novel glycosylation-based biomarkers from the serum glycoproteome under investigation as cancer diagnostics and for monitoring and prognostics and includes details of recent high throughput and other emerging glycoanalytical techniques.

Alpha fetoprotein mediates HBx induced carcinogenesis in the hepatocyte cytoplasm

Although tumor-associated fetal protein AFP has demonstrated utility as a clinical tumor marker, the significance of intracellular AFP is still unclear. The aim of this study was to explore the role of cytoplasmic AFP during HBx induced carcinogenesis, which had not previously been recognized; 614 HCC patients were analyzed for correlation of HBV infection with AFP level, and much higher AFP levels were found in HBsAg positive patients. Tumor tissue specimens from 20 HCC patients were used for analysis of AFP and GADD45α. Analysis of HCC specimens showed that upregulation of cytoplasmic AFP is associated with down-regulation of GADD45α in neoplastic tissue. Transfected HBx promotes transcription of AFP by acting on the elements in the AFP gene regulatory region. HBx itself did not directly impact transcription of GADD45α. However, the obstruction of RAR signaling by HBx induced elevation of AFP, which led to down-regulation of GADD45α. Cytoplasmic AFP was able to interact with RAR, disrupting its entrance into the nucleus and binding to the elements in the regulatory region of the GADD45α gene. Knockdown of AFP in siRNA-transfected AFP positive cell lines was synchronously associated with an incremental increase of RAR binding to DNA, as well as upregulation of GADD45α and it was contrary in AFP gene-transfected AFP negative cell lines. These results indicate cytoplasmic AFP is not only a histochemical tumor biomarker for human hepatoma but is also an intracellular signal molecule and potential participant in HBx induced hepatocarcinogenesis.

Engineering α-fetoprotein-based gene vaccines to prevent and treat hepatocellular carcinoma: review and future prospects

Activation of a patient's immune system offers an attractive approach to prevent and treat hepatocellular carcinoma (HCC). However, the antitumor efficacy of current HCC vaccines was weak owing to insufficient immune activation of targeting self/tumor antigens. We recently found that epitope-optimized α-fetoprotein effectively activated CD8 T cells and generated potent antitumor effects in the carcinogen-induced autochthonous HCC mouse model. We predict that the same antigen engineering approach of epitope-optimization will enable us to develop effective human vaccines to prevent HCC recurrence after liver resection. The engineered human HCC vaccines may also allow us to identify high-affinity T-cell receptors and antibodies that can be used to reprogram T cells to treat HCC tumors via adoptive transfer.

Alpha-fetoprotein: a renaissance

Alpha-fetoprotein (AFP) is a major mammalian embryo-specific and tumor-associated protein that is also present in small quantities in adults at normal conditions. Discovery of the phenomenon of AFP biosynthesis in carcinogenesis by G. Abelev and Yu. Tatarinov 50 years ago, in 1963, provoked intensive studies of this protein. AFPs of some mammalian species were isolated, purified and physico-chemically and immunochemically characterized. Despite the significant success in study of AFP, its three-dimensional structure, mechanisms of receptor binding along with a structure of the receptor itself and, what is the most important, its biological role in embryo- and carcinogenesis remain still obscure. Due to difficulties linked with methodological limitations, research of AFP was to some extent extinguished by the 1990 s. However, over the last decade a growing number of investigations of AFP and its usage as a tumor-specific biomarker have been observed. This was caused by the use of new technologies, primarily, computer-based and genetic engineering approaches in studying of this very important oncodevelopmental protein. Our review summarizes efforts of different scientific groups throughout the world in studying AFP for 50 years with emphasis on detailed description of recent achievements in this field.

Impact of intracellular alpha fetoprotein on retinoic acid receptors-mediated expression of GADD153 in human hepatoma cell lines

The aim of our study was to gain a better understanding of the molecular mechanism underlying the previously unrecognized role of cytoplasmic alpha fetoprotein (AFP) in retinoic acid receptors (RAR) mediated expression and biological effects of GADD153. Using microarray analysis, the expression of the GADD153 gene showed the greatest fold change among apoptosis/growth related genes in response to ATRA. AFP was able to interact with RAR in HepG2 cells, which was undetectable in HLE cells owing to absence of AFP. ATRA promoted nuclei entrance of RAR, expression of GADD153 and apoptosis, and these changes were reversed after transfection with the afp gene or addition of AGN193109. The level of GADD153 was gradually elevated as the effect of AFP was counteracted by increasing dose or prolonging treatment time with ATRA in HepG2 cells. Knockdown of AFP in siRNA-transfected HepG2 cells or over-expression of AFP in afp gene-transfected HLE cells was synchronously associated with up-regulation or down-regulation, respectively, of GADD153 expression. Both ATRA administration and AFP knockdown were each able to promote greater binding of RAR to its response element with consequent elevation of the proportion of apoptotic cells. Conversely, transfection of HLE cells with pcDNA3.1-afp resulted in apparent reduction of RAR binding to DNA and change of biological effect. These data taken together demonstrate the involvement of AFP in RAR-mediated expression and biological effects of GADD153. These findings provide a novel insight into the mechanism underlying the impact of AFP on the RAR signal network.

Dendritic cell-based vaccines positively impact natural killer and regulatory T cells in hepatocellular carcinoma patients

Immunotherapy of cancer must promote antitumor effector cells for tumor eradication as well as counteract immunoregulatory mechanisms which inhibit effectors. Immunologic therapies of cancer are showing promise, including dendritic cell-(DC-) based strategies. DC are highly malleable antigen-presenting cells which can promote potent antitumor immunity as well as tolerance, depending on the environmental signals received. Previously, we tested a peptide-pulsed DC vaccine to promote Alpha-fetoprotein (AFP-) specific anti-tumor immunity in patients with hepatocellular carcinoma (HCC), and reported on the CD8⁺ T cell responses induced by this vaccine and the clinical trial results. Here, we show that the peptide-loaded DC enhanced NK cell activation and decreased regulatory T cells (Treg) frequencies in vaccinated HCC patients. We also extend these data by testing several forms of DC vaccines in vitro to determine the impact of antigen loading and maturation signals on both NK cells and Treg from healthy donors and HCC patients.

Mechanism of Cancer Growth Suppression of Alpha-Fetoprotein Derived Growth Inhibitory Peptides (GIP): Comparison of GIP-34 versus GIP-8 (AFPep). Updates and Prospects

The Alpha-fetoprotein (AFP) derived Growth Inhibitory Peptide (GIP) is a 34-amino acid segment of the full-length human AFP molecule that inhibits tumor growth and metastasis. The GIP-34 and its carboxy-terminal 8-mer segment, termed GIP-8, were found to be effective as anti-cancer therapeutic peptides against nine different human cancer types. Following the uptake of GIP-34 and GIP-8 into the cell cytoplasm, each follows slightly different signal transduction cascades en route to inhibitory pathways of tumor cell growth and proliferation. The parallel mechanisms of action of GIP-34 versus GIP-8 are demonstrated to involve interference of signaling transduction cascades that ultimately result in: (1) cell cycle S-phase/G2-phase arrest; (2) prevention of cyclin inhibitor degradation; (3) protection of p53 from inactivation by phosphorylation; and (4) blockage of K+ ion channels opened by estradiol and epidermal growth factor (EGF). The overall mechanisms of action of both peptides are discussed in light of their differing modes of cell attachment and uptake fortified by RNA microarray analysis and electrophysiologic measurements of cell membrane conductance and resistance. As a chemotherapeutic adjunct, the GIPs could potentially aid in alleviating the negative side effects of: (1) tamoxifen resistance, uterine hyperplasia/cancer, and blood clotting; (2) Herceptin antibody resistance and cardiac (arrest) arrhythmias; and (3) doxorubicin's bystander cell toxicity.

Biological functions of alpha-fetoprotein

Alpha-fetoprotein (AFP) is a well-known biomarker for the diagnosis of hepatocellular carcinoma. Extracellular AFP can act as a carrier to transport a variety of ligands or as a growth regulator to control the growth of tumor cells, while intracellular AFP can bind to and interact with transcription factors or some key proteins and function as a signal molecule to regulate cell proliferation or apoptosis. This paper provides novel insights into the mechanisms underlying the role of AFP in carcinogenesis and tumor chemotherapy.

Kinase inhibitor Sorafenib modulates immunosuppressive cell populations in a murine liver cancer model

Accumulating evidence suggests that regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSC) are elevated in cancer patients and tumor-bearing hosts, and that depletion of Tregs and MDSC may enhance the anti-tumor immunity of the host. Sorafenib, a novel multi-kinase inhibitor, is approved for the treatment of several human cancers, including advanced hepatocellular carcinoma (HCC). Sorafenib is believed to inhibit tumor growth via anti-angiogenesis, cell cycle arrest, and inducing apoptosis. However, the impact of Sorafenib on immune cell populations in tumor-bearing hosts is unclear. In this report, we show that Tregs and MDSC are increased in the spleens and bone marrows of the BALB/c mice with liver hepatoma. The increase in Tregs and MDSC was positively correlated with tumor burden. Treatment of Sorafenib not only inhibited HCC cell growth in mice but also significantly decreased the suppressive immune cell populations: Tregs and MDSC. In conclusion, our study strongly suggests that Sorafenib can enhance anti-tumor immunity via modulating immunosuppressive cell populations in the murine liver cancer model.

Immunoregulatory effects of AFP domains on monocyte-derived dendritic cell function

Background

Alpha-fetoprotein (AFP) is a tumor-associated glycoprotein that functions in regulation of both ontogenic and oncogenic growth. Recent study showed that AFP can induce apoptosis or impair monocyte-derived dendritic cell (MDDC) function. However, it is still unclear which AFP domain (D-AFP) plays major role in this function.

Results

As expected monocytes cultured in the presence of Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) and Interleukin-4 (IL-4) developed into MDDC. Up-regulation of HLA-DR and CD11c as well as loss of CD14 molecules could be observed. Full length AFP (FL-AFP), domain 2 AFP (D2-AFP) and D3-AFP, but not D1-AFP, significantly inhibited the expression of HLA-DR^high/CD11c^high and CD80⁺/CD86^high molecules. In contrast, CD83 expression was substantially down-regulated in all samples. Expression of CD40 was significantly suppressed by FL-AFP but not by any D-AFPs. Finally, both FL-AFP and D-AFP impaired the MDDC ability to secrete IL-12 (p70).

Conclusions

D2- and D3- but not D1-AFP extensively suppresses the MDDC function. All the recombinant AFP proteins impaired the ability of MDDC to secrete IL-12.

Alpha-fetoprotein: a new member of intracellular signal molecules in regulation of the PI3K/AKT signaling in human hepatoma cell lines

Despite its well-defined role as a serum growth factor during fetal liver development and hepatic oncogenesis, the biological significance of cytoplasmic alpha-fetoprotein (AFP) remains incompletely understood. Here, we provide evidence to illustrate that cytoplasmic AFP may function as a regulator in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway in human hepatocellular carcinoma cells. The results demonstrated colocalization and interaction of AFP and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in the cytoplasm of AFP-producing Bel 7402 and HepG2 cells, with an interaction distance of 12.6 ± 2.7 Å as determined with the fluorescence resonance energy transfer technique. Knockdown of AFP mRNA or inhibition of AFP expression by all trans-retinoic acid resulted in enhancement of the PTEN level with a synchronous decrease in phosphorylated AKT. Transfection of the afp gene into HLE cells (originally AFP negative) led to a significant activation of AKT signaling. The inhibition of PI3K signaling by LY 294002 was simultaneously reversed by transfection, accompanied by diminution of all trans-retinoic acid-induced upregulation of PTEN and enhancement of cell growth. In conclusion, these results demonstrate that cytoplasmic AFP is involved in regulation of hepatocellular growth and tumorigenesis.